Here's what you need to know about Sally Yates, who defied Trump and was instrumental in getting Michael Flynn fired

Sally Yates, the former acting attorney general, made waves after she sparred with Sen. Ted Cruz on Monday during her testimony at a Senate Judiciary subcommittee hearing on Russia's interference in the 2016 election.

While her exchange with Cruz went viral in political circles, Yates was testifying to address reports as to whether she warned the White House in January about ousted National Security Advisor Michael Flynn's ties to Sergey Kislyak, the Russian ambassador to the US.

Yates said she informed the White House that Flynn could be vulnerable to Russian blackmail just days after Trump's inauguration.

Trump still chose Flynn for the national security advisor post. Flynn, however, was fired less than a month into his tenure after he admitted to misleading Vice President Mike Pence about his conversations with Kislyak.

Yates' journey from relative obscurity to Democrat darling happened quickly. Following her warnings over Flynn, she defied Trump's now-infamous "travel ban," which led to her firing in January.

Here's what you need to know about Sally Yates, from her rise through the ranks of the Department of Justice, to her crucial testimony on Monday.

Justice Department beginnings

Yates started her career at the Justice Department three years after graduating from the University of Georgia's law school.

She spent over three decades at the agency, working her way up to district attorney in Georgia's northern district after prosecuting a series of white collar cases, according to CNN. Yates was the first woman to hold that position.

Yates successfully aided the prosecution of Eric Rudolph, who was accused of bombing Centennial Olympic Park in Atlanta during the 1996 Olympics.

After Eric Holder retired, Obama nominated Loretta Lynch to take Holder's top spot at the Justice Department, with Yates for deputy. Yates was easily confirmed with bipartisan support.

Jeff Sessions, now the attorney general, was one of the few hardline conservatives to vote against Lynch's confirmation.

Protesters assemble at John F. Kennedy International Airport in New York, Saturday, Jan. 28, 2017, after earlier in the day two Iraqi refugees were detained while trying to enter the country. Associated Press/Craig Ruttle

Travel ban backlash

Yates become a household name after Trump fired her for refusing to cooperate with the White House's first iteration of the executive order temporarily halting refugees and citizens from seven majority-Muslim countries from entering the US in January.

The Yates-led Justice Department said it was caught by surprise by the travel ban.

Yates, then acting attorney general, refused to direct the Justice Department to comply with the executive order, calling it "unlawful" and "indefensible" in court, according to CNN. She added that Trump had undermined the ban's legal grounds by discussing how it was meant to single out Muslims. Trump made those comments while on the campaign trail.

The White House released a statement days later, saying Yates had "betrayed the Department of Justice" by refusing to enact the order. Yates was fired via a hand-delivered letter on Tuesday, January 31 — just four days after she refused to comply with Trump's order.

During her testimony to the Senate on Monday, Yates said the Justice Department wasn't consulted prior to Trump signing the executive order, and that she learned about it "through media reports," per The New York Times.

Former National Security Adviser Michael Flynn, arrives for the President Donald Trump, Japanese Prime Minister Shinzo Abe joint new conference in the East Room of the White House, in Washington, Friday, Feb. 10, 2017. AP Photo/Carolyn Kaster

Michael Flynn, blackmail, and the Russian ambassador

Yates visited the White House shortly after Trump's inauguration, where she told Trump's chief counsel, Don McGahn, that she had "serious concerns" about Flynn.

Yates testified on Monday that she told McGahn that Flynn could be vulnerable to Russian blackmail after he misled Pence about his contacts with Kislyak, the Russian ambassador.

"To state the obvious: You don't want your national security adviser compromised with the Russians," Yates told the Senate subcommittee.

It goes even deeper. Obama reportedly warned Trump about hiring Flynn when the two met at the White House in November following the election. Obama himself had previously fired Flynn from the Defense Intelligence Agency in 2014. And New Jersey Gov. Chris Christie, who lead Trump's transition team for a brief period, stated that he didn't "see eye-to-eye" with Flynn, Politico reported.

"Would you agree that is broad statutory authorization?" Cruz asked Yates in attempting to make a point that Yates' refusal to comply with Trump's travel ban was a matter of partisan politics.

Yates shot back, bringing up a different provision from the INA that says that "no person shall receive preference or be discriminated against in issuance of a visa because of race, nationality or place of birth."

She added that her concern with the travel ban was not whether it complied with the INA, but whether it violated the Constitution's equal protection clause. Yates maintained that it was important to look at the "intent" behind Trump's actions prior to signing the order.

"And the intent is laid out in his statements," Yates said, obliquely referring to statements Trump made on the campaign trail about protecting the US from Muslim terrorists.

Cruz then asked if Yates was aware of any similar situation in the DOJ's history in which an attorney general ordered the department not to follow a policy handed down from the White House Office of Legal Counsel.

"I'm not," she said. "But I'm also not aware of a situation where the OLC was advised not to tell the AG about it until after it was over."

"I don't think you can think of any possible candidates in Georgia and not mention Sally Yates' name right now," Tharon Johnson, who was the national southern regional director for Obama's 2012 campaign, told Politico in February.

"She's a symbol of hope and resistance when it comes to standing up to Donald Trump," he said.